Compositions comprising a homopolymer of acrylamide and an organic acid



United States Patent 055cc rammed July 2, 1957 COMPOSITIONS COMPRISING A HOMOPOLYMER OF ACRYLAMIDE AND AN ORGANIC ACID No Drawing. Application June 22, 1954, Serial No. 438,604

Claims. (Cl. 260-31.2)

This invention relates to new and useful compositions of matter and more particularly to compositions comprising an acrylamide polymerization product and at least "one acid selected from the class consisting of glacial acetic acid, chloroacetic acids (mono-, di-, and trichloroacetic acids), propionic acid, acrylic acid, glycolic acid and lactic acid. More particularly the invention is concerned with such compositions wherein the acid, more particularly organic acid, is compatible with and forms a solution (homogeneous mixture) with the acrylamide polymerization product; or, otherwise stated, the said polymerization product is dissolved in the said acid. The aforesaid acids function as a solvent, swelling agent, or plasticizer for the acrylamide polymerization product.

The compositions of this invention in which one of the aforesaid acids, or a mixture thereof in any proportions, is employed primarily as a solvent or swelling agent for the acrylamide polymerization product, in which case it constitutes a major proportion (more than 50%), e. g., from 55 to 99% or more, by weight of the composition, are particularly useful in the production of shaped articles therefrom, e. g., filaments, films, threads, rods, tubes, and the like, or as coating, adhesive, laminating, impregnating, paper-treating, textile-treating compositions, etc., or as components of such compositions. An acid of the kind aforementioned also may be used primarily as a plasticizer for an acrylamide polymerization product, in which case it usually constitutes a minor proportion (less than 50%), e. g., from 0.5 to 45%, generally from 1 to 35 or 40%, by weight of the composition. If the product is used or intended for use in an application where water-insolubility is important, it can be rendered waterinsoluble by suitable treatment or modification, as by' cross-linking with a cross-linking agent, e. g., methylenebis-acrylamide, diallyl phthalate, etc.

Polymers and copolymers of acrylamide were known prior to our invention. Likewise, it was known that homopolymeric acrylamide and many of the copolymers of acrylamide are soluble in water. However, to the best of our knowledge and belief it was not known prior to our invention that acrylamide polymerization products could be dissolved or swollen in certain organic solvents.

' Thus, in a recent article by Shulz et al., Studies on the Radical Polymerization of Acrylamide, [Makromol. Chem. 12, 20-34 (1954)], the authors state: The polyacrylamides prepared by the polymerization methods that we have described are soluble in water, but insoluble in ordinary solvents such as alcohols, esters, ethers, and hydrocarbons. Among the organic compounds specifically mentioned by the authors as being non-solvents for polyacrylamide are tetrahydrofuran, dimethylformamide, nitrobenzene, bromobenzene, and tetralin.

The present invention is based on our discovery that polymers or copolymers of acrylamide, more particularly polymeric (homopolymeric) acrylamide and thermoplastic copolymers of acrylamide, specifically such copolymers containing in their molecules an average of at least 75% by weight of combined acrylamide, e. g., copolymers of, by weight, from to 99.5% of acrylamide and am other monomer such, for instance, as vinyl acetate, methyl acrylate, ethyl acrylate, acrylic acid, etc., are compatible with glacial acetic acid, mono-, diand trichloroacetic acids, propionic acid, acrylic acid, glycolic acid, and lactic acid, and with mixtures of such acids in any proportions; and upon our further discovery that such acids are capable of dissolving or swelling the acrylamide polymerization product to yield solutions or swollen masses which are suitable for use in a wide variety of industrial applications, examples of which have been given hereinbe'fore. The invention is based on our additional discovery that the aforementioned acids or mixtures thereof are able eifectively to plasticize acrylamide polymerization products so that the latter more easily can be shaped, as by extrusion or molding, or cast into useful articles of manufacture. The acid employed in practicing our invention may be used either as a temporary modifier (more particularly, as a temporary plasticizer), that is, a modifier which subsequently is removed from the polymerization product, or as a permanent modifier, specifically plasticizer, which is permitted to remain in the acrylamide homopolymer or copolymer.

The unobvious nature of our invention will be immediately apparent to those skilled in the art when it is considered that polyacrylamide does not dissolve upon being admixed with any of a large number of organic compounds, even when heated at C. for /2 hour or when heated to boiling and then at boiling for about 10 min utes in the case of those compounds boiling under 120 C. Thus we have found that finely ground polyac'rylamide does not dissolve, swell, or coalesce, when heated under the aforementioned conditions, in each of the following compounds:

Isoamyl alcohol Methacrylic acid Diethylene glycol mono- Butyrolactone ethyl ether Pyrrol-idone Cresol 2-Methyldioxolane Diethylene glycol Dioxane Cyclohexanol Sulfolane Tetrahydrofurfuryl alcohol Nitroethane Ethylene glycol monoethyl Ethylene carbonate ether Ethylene sulfite Monoethylene glycol mon- Diallyl carbamate oethyl formal Triallyl cyanurate Acetonitrile fi-Cyanoethyl acetate Trichloroacetonitrile Dibutyl phthalate Acrylonitrile Triethyl phosphate Succinonitrile Trimethyl orthoformate Dimethylformamide Ethylene chlorohydrin Dimethylcyanamide Epichlorohydrin Diethylthiophosphonamide Diacetyl Triethanolamine Tetrahydrofuran Triethylenetetramine Pentaerythritol dipropional Acetic anhydride Chloromaleic anhydride Maleic anhydride Methyl ethyl ketone Homopolymeric acrylamide and acrylamide copolymers (thermoplastic acrylamide copolymers) containing in the polymer molecules an average of at least 75% by weight of combined acrylamide are employed in carrying the present invention into effect. These polymers and copolymers are prepared by methods now well known to those skilled in the art. In some cases the polymerization rates of the individual monomers in a polymerizable mixture may be different, with the result that the proportions of the components in the final copolymer are different from the proportions thereof in the mixture of monomers which are polymerized. The proportions of monomers in the polymerizable mixture therefore are preferably adjusted, in practicing the present invention, so that the final copolymer contains in the molecules thereof an average of at least at 75% by weight of combined acrylamide. The acrylamide polymerization product may be one in which, for example, a homopolymer of acrylamide has been modified by introducing one or more other groups into the polymer molecule. For example, the acrylamide polymerization product may be one in which liomopolymeric acrylamide or certain copolymers of acrylamide have been hydrolyzed under acid or alkaline conditions to introduce carboxylic acid or salt groups into the polymer molecule or structure, or has been reacted with an aldehyde, specifically formaldehyde, to introduce alkylol, more particularly methylol, groups into the polymer structure. In such instances, the extent of hydrolysis or alkylolation or other modifications is so controlled that the acrylamide polymerization product still contains at least 75 by weight of acrylamide units. The expression polymerization product containing in the polymer molecules an average of at least 75% by weight of combined acrylamide, as used herein and in the appended claims, means, therefore, a polymerization product (polymer, copolymer or interpolymer, graft polymer, or polymer modified by the introduction of other groups, etc., or mixture thereof) containing in the molecules thereof an average of at least 75 by weight of the acrylamide unit, which is considered to be present in the individual polymer molecule as the group I CH -CHCONH or, otherwise stated, at least 75 by weight of the reactant substance converted into and forming or comprising the polymerization product is acrylamide.

Illustrative examples of monomers which may be copolymerized with acrylamide to yield a polymerization product containing in the polymer molecules an average of at least 75 by weight of combined acrylamide are compounds containing a single CH2=C grouping, for instance, the vinyl esters and especially the vinyl esters of saturated aliphatic monocarboxylic acids, e. g., vinyl acetate, vinyl propionate, vinyl butyrate, etc.; vinyl and vinylidene halides, e. g., the vinyl and vinylidene chlorides, bromides and fluorides; allyl-type alcohols, e. g., allyl alcohol, methallyl alcohol, ethallyl alcohol, etc.; allyl, methallyl and other unsaturated monohydric alcohol esters of monobasic acids, e. g., allyl and methallyl acetates,

laurates, cyanides, etc.; acrylic and alkacrylic acids (e.,g., methacrylic, ethacrylic, etc.) and esters and amides of such acids other than acrylamide (e. g., methyl, ethyl, propyl, butyl, etc., acrylates and methacrylates, methacrylamide, N-methyl, -ethyl, -propyl, -butyl, etc., acrylamides and methacrylamides, etc.); methacrylonitrile, ethacrylonitrile and other hydrocarbon-substituted acrylonitriles; unsaturated aliphatic hydrocarbons containing a single CH2=C grouping, e. g., isobutylene, etc., and numerous other vinyl, acrylic and other compounds containing a single CH2=C grouping which are copolymerizable with acrylamide to yield thermoplastic copolymers. Alpha, beta-unsaturated polycarboxylic acids and alkyl esters thereof also may be copolymerized with acrylamide to form copolymers which are useful in practicing the present invention, e. g., maleic, fumaric, citraconic, itaconic, etc., acids, and the dimethyl, -ethy1, -propyl, -butyl, etc., esters thereof.

The polymeric and copolymeric acrylamides used in practicing our invention may be of any suitable molecular weight, but ordinarily the molecular weight (weight aver age molecular weight) is not less than 10,000 and may be as high as 2 million or more. Ordinarily the weight average molecular weight is within the range of about 70,000 or 80,000 to 1,600,0002,000,000. Such molecular weights (weight average molecular weights) are determined in the manner described more fully by P. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, chap. 7, p. 266 et seq. Briefly described the values are ascertained by calculating intrinsic viscosities (limiting viscosity numbers) from measurements of flow times in an Ostwald viscosimeter at 300 C. of any four concentrations of the acrylamide polymerization product below 0.5 g./ ml. in water or 1 N sodium nitrate solution. The relation between the intrinsic viscosity and the weight average molecular weight is previously established by light-scattering measurements on a set of eight samples of pure polyacrylamide, in water, ranging in weight average molecular weight from 78,700 to 1,640,000. The light-scattering measurements are performed on solutions filtered through ultrafine sintered glass and are interpreted by standard light-scattering procedures and corrected by determinations of dissymmetries and depolarization ratios.

The dissolution of the acrylamide polymerization product in, or swelling by, the acid employed in practicing the present invention is accelerated by using a polymer or copolymer of acrylamide which is in a finely divided state, e. g., one which, if not in a finely divided state as originally formed, has been ground so that all or substantially all of it will pass through a U. S. standard sieve series No. 50 screen. It also is usually desirable to agitate the mass, as by mechanical stirring, while admixing the polymerization product with the solvent. To avoid or minimize discoloration of the polymeric or copolymeric acrylamide, it is generally advantageous to employ the lowest possible temperature in effecting dissolution, swelling or plasticization of the acrylamide polymerization product, which temperature is consistent with practical considerations, e. g., the time required for effecting solution (or other desired result), etc.

The proportions of the acrylamide polymerization product and the acid in the compositions of our invention may be varied widely, depending mainly upon the particular use for which the composition is intended. If the acid (or mixture of acids in any proportions) is employed primarily as a solvent for the acrylamide homopolymer or copolymer so as to obtain, for example, a film or other shaped article, or to make a coating, impregnating, laminating, adhesive, textile-treating composition, etc., from which all or substantially all of the solvent subsequently is removed, then the acrylamide polymerization product usually constitutes at least 1%, but less than 50%, e. g., from 5% to about 25 or 30%, by weight of the solution. Advantageously, in most cases, when the solution is to be used in, for example, the casting of films, the polymer or copolymer of acrylamide constitutes at least 5% by weight of the solution.

The solutions of the acrylamide polymerization product in the acids used in practicing the present invention are especially adapted for casting in the form of films. For instance, a solution of the acrylamide polymerization product in glacial acetic acid may be cast upon a revolving drum which is partly immersed in a coagulating bath of, for example, acetone, methyl alcohol, ethyl alcohol, dioxane or dimethylformamide, and which will serve to deposit the polymerization product as a thin film on the drum as it passes through the bath.

If the acid is to be employed primarily as a plasticizer for the acrylamide polymerization product, then the acid generally constitutes less than 50%, e. g., from 1% to 35 or 40%, by weight of the composition (acid plus polymer or copolymer of acrylamide).

The aforementioned ranges of proportions are mentioned as indicative of proportions that may be employed in forming solutions of, or plasticized compositions containing, the acrylamide polymerization product, and our invention obviously is not limited to the'use of only such proportions. The important factor is that the proportions be such that the viscosity or plasticity of the composition at the particular operating temperature (that is, the temperature at which the composition is employed) be within a workable range for the particular use to which the composition is to be placed.

In order that those skilled in the art may better understand how -the present invention can be carried into effect, the following examples are given by way of illustration and not by way of limitation. All parts and percentages are by weight unless otherwise stated.

Example 1 One (1) part of dry homopolymeric acrylamide, ground so that substantially all of it passes through a U. S. Standard Sieve Series No. 50 screen, is thoroughly mixed with 99 parts of lactic acid (dl). (The polyacrylamide employed has a weight average molecular weight of about 200,000 as determined by the method hereinbefore described, that is, by viscometric data related to previous light-scattering measurements.) The mixture is allowed to stand at room temperature (about 20-30 C.) for three days, at the end of which period of time the polyacrylamide has completely dissolved to form a clear solution. This solution can be cast to yield films as hereinbefore described. Films of plasticized homopolymeric acrylamide are obtained by allowing a substantial amount of lactic acid to remain in the film, e. g., from 1 or 2% to 35 or 40% or more by weight of the film.

If water-resistant films are desired, they can be obtained by immersing the film (before or after removal of all or part of the lactic acid) in an aqueous solution of formaldehyde to form the N-methylol derivative of the polyacrylamide, followed by heating at 120-150 C. to obtain a water-insoluble, cross-linked material.

Example 2 Same as in Example 1 with the exception that there is used 99 parts of acrylic acid instead of 99 parts of lactic acid. Similar results are obtained.

Example 3 Same as in Example 1 with the exception that, instead of 1 part of homopolymeric acrylamide, there is employed 1 part of a dry, finely divided copolymer of about 75% acrylamide and about 25% of (a) vinyl acetate, or (b) methyl acrylate, or (c) styrene, or (d) methacrylonitrile, or (e) methacrylamide. Similar results are obtained.

Example 4 One (1) part of finely ground homopolymeric acrylamide, such as was employed in Example 1, and 99 parts of monochloroacetic acid are mixed thoroughly together and heated at 120 C. for 30 minutes. At the end of this period of time the polyacrylamide is visibly swollen. After standing for several weeks at room temperature, the polymer dissolves completely upon again heating the mixture at 120 C. for a few minutes.

Example 5 Same as in Example 4 with the exception that 1 part of dichloroacetic acid is used in one instance, and 1 part of trichloroacetic acid is employed in another case, instead of 1 part of monochloroacetic acid. Similar results are obtained.

Instead of using mono-, di-, or trichloroacetic acid alone, as described in Example 4 with reference to monochloroacetic acid, and as has just been described in this example with reference to the other acids, we may use mixtures of any or all of these chloroacetic acids in any proportions.

Example 6 Same as in Example 4 with the exception that 1 part of propionic acid is used in one case, and 1 part of glycolic acid is employed in another instance, instead of 1 part of monochloroacetic acid. Similar results are obtained.

Example 7 One (1) gram of finely ground homopolymeric acrylamide, such as was employed in Example 1, is added to 100 ml. of a 50/50 mixture, by volume, of glacial acetic acid and formamide. The mixture is heated at 120 C.

for 30 minutes, yielding a swollen mass of polyacrylamide. A clear, homogeneous solution of the polyacrylamide in the above solvent mixture is obtained by allowing the mass to stand for about two weeks at room temperature.

Example 8 Same as in Example 7 with the exception that there is used a 50/50 mixture, by volume, of glacial acetic acid and urea instead of a 50/50 mixture, by volume, of glacial acetic acid and formamide. Similar results are obtained.

Example 9 One (1) gram of a dry, ground copolymer of about 90% acrylamide and 10% acrylic acid is added to 100 ml. of glacial acetic acid. The resulting mixture is heated at 120 C. for 30 minutes, yielding a swollen acrylamideacrylic acid copolymer When the swollen mass is allowed to remain in the excess glacial acetic acid for one week at room temperature (2030 C.), a clear, homogeneous solution is obtained.

Example 10 Same as in Example 9 with the exception that 100 ml. of monochloroacetic acid is used instead .of 100 ml. of glacial acetic acid; also, after the initially heated mixture has stood at room temperature for one week, it is heated again at 120 C. for a few minutes. A clear, homogeneous solution is obtained.

Example 11 heating at 120 C. for 30 minutes, the polyacrylarnide completely dissolves in the glacial acetic acid to form a clear, homogeneous solution. This solution can be cast to yield films as hereinbefore described.

Example 12 Same as in Example 11 with the exception that, instead of 1 part of homopolymeric acrylamide, there is employed 1 part of a dry, finely divided copolymer of about 75 acrylamide and about 25% of (a) vinyl acetate, or (b) methyl acrylate, or (c) styrene, or (d) methacrylonitrile, or (e) methacrylamide. Similar results are obtained.

It will be understood, of course, by those skilled in the art that our invention is not limited to the specific ingredients and methods of effecting solution of the polymer or copolymer of acrylamide that are given by way of illustration in the foregoing examples. Thus, instead of the specific comonomers employed in Examples 3, 9, 10 and 12 in forming copolymers with acrylamide, we may use any other comonomer which is copolymerizable with acrylamide in the proportions hereinbefore set forth, that is, in proportions such that the finished copolymer contains in the molecules thereof at least about 75% by weight of combined acrylamide. Numerous examples of such comonomers were given previously in the specification.

The advantages of the present invention will be immediately apparent to those skilled in the art from the foregoing description. The invention broadens the field of utility of polyacrylamide, since it provides solvents and plasticizers therefor, other than water, and thus makes the resulting compositions suitable in applications for which aqueous solutions of polyacrylamide would be entirely unsuited. As is well known, aqueous solutions of polyacrylamide are polar and have a high dielectric constant; Consequently, such solutions are entirely unsuitable for many applications.

As a result of the present invention all of the inherent advantages of a non-aqueous solvent or swelling agent can be utilized in Working with polyacrylamide (homopolymeric acrylamide) and with copolymers of acrylamide containing at least about 75% by weight of acrylamide combined in the polymer molecule. For instance, the invention provides compositions which can be extruded or otherwise shaped to form useful articles of manufacture. The compositions of the present invention are also useful in warp-sizing and other textile-treating applications, as Well as in adhesive compositions, ceramic binders, nitrocellulose lacquers, as components of rubberbased glues, in furniture glues which are capable of withstanding freeze-thaw cycles, in making chemical analyses of polymers and copolymers of acrylamide where it is desirable to make the analysis in a non-aqueous solvent for the acrylamide polymerization product, and for various other purposes, numerous examples of which have been given hereinbefore.

We claim:

1. A composition of matter comprising (1) homopolymeric acrylamide and (2) at least one acid selected from the class consisting of glacial acetic acid, chloroacctic acids, propionic acid, acrylic acid, glycolic acid and lactic acid. 7

2. A composition as in claim 1 wherein the homopolymeric acrylamide of (1) constitutes at least 1% by weight 3 of the composition.

3. A composition of matter comprising (1) homopolymeric acrylamide and (2) glacial acetic acid.

v 8 V 4. A composition of matter comprising (1) homopoly-' meric acrylamide and (2) a chl-oroacetic acid.

5. A composition of matter comprising (1) homopolymeric acrylamide and (2) propionic acid.

6. A composition of matter comprising (1) homopolymeric acrylamide and (2) acrylic acid.

7. A composition of matter comprising (1) homopolymeric acrylamide and (2) lactic acid.

8. A composition of matter comprising (1) homopolymeric acrylamide and (2) glacial acetic acid, the homopolymeric acrylamide of (1) constituting from about 1% to about 30%, by Weight, of the total amount of (l) and (2).

9. A composition of matter comprising (1) homopolymeric acrylamide and (2) a chloroacetic acid, the homopolymeric acrylamide of (1) constituting from about 1% to about 30%, by weight, of the total amount of (1) and (2). 1

10. A plasticized composition comprising homopolymeric acrylamide, said homopolyrneric acrylamide being plasticized with a plasticizing amount not substantially exceeding 40% by weight of the composition of a plasticizer comprising at least one acid selected from the class consisting of glacial acetic acid, chloroacetic acids, propioni'c acid, acrylic acid, glycolic acid and lactic acids.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A COMPOSITION OF MATTER COMPRISING (1) HOMOPOLYMERIC ACRYLAMIDE AND (2) AT LEAST ONE ACID SELECTED FROM THE CLASS CONSISTING OF GLACIAL ACETIC ACID, CHLOROACETIC ACIDS, PROPIONIC ACID, ACRYLIC ACID, GLYCOLIC ACID AND LACTIC ACID. 